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Individual and societal risk

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Sruthi Madhu

This document discusses quantitative risk determination methods. It provides equations to calculate individual risk and societal risk for a scenario involving three cylinders containing LPG, cyclohexane, and benzene. The individual risk is calculated at four points around the facility using frequency of incidents and probability of fatality values. The societal risk is calculated based on estimated affected populations and probabilities of fatality.

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PRESENTED BY SRUTHI P M MTECH HSE 1
INTRODUCION 2
Risk: The likelihood of a specific effect within a specific period. There are two methods of risk determination Qualitative risk determination Quantitative risk determination 3
QUANTITATIVE RISK DETERMINATION Risk indices are single numbers or tabulation of numbers which are correlated to the magnitude of risk. Some risk indices are relative values with no specific units, which only have meaning within the context of the risk index calculations. The main two risk sets are Individual risk Societal risk 4
Individual risk(IRx,y): Probability of death per year of exposure to an individual at a certain distance from the hazardous source. It is usually expressed in the form of iso-risk contours. IR x,y =裡IR (x,y,i) IR (x,y,i)= 裡fi*pfi Pfi is obtained using probit equation. AlChe/CCPS is used for converting probit equation to probability ie pfi 5
Different probit functions used for calculation The probit models are generally expressed as Pr =k1+k2(ln V) Probit equations are available for a variety of exposures, including exposure to toxic materials, heat, pressure and radiation,impact and sound. P=a+bln cnt Esignberg also provides a probit function for fatalities due to direct effect of overpressure as follows. Pr=-77+6.91(ln P0) For first degree burn Pr= -39.83+3.0186ln (q4/3t) For lethality Pr=-36.38+2.56 ln tq4/3 6
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Societal risk: Societal risk is a measure of risk to a group of people. It is most often expressed in terms of the frequency distribution of multiple casualty events. (FN curve). Number of people affected by all incident outcome cases can be estimated using the following equation Ni=裡P (x,y)*pfi 8
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There are three cylinders in a factory. First cylinder is filled with LPG in the horizontal cylinder. Second cylinder is filled with cyclohexane in the vertical cylinder. Third cylinder is filled with Benzene in the vertical cylinder. The wind speed in the region is 4.1 m/s. The ambient temperature is 25C. Determine the individual risk and societal risk. 10
Assume the values of frequencies of incident outcome cases as BLEVE of LPG -8x10-4 VCE of cyclohexane -6x10-5 Pool fire of Benzene-2.67x10-4 11
BLEVE of LPG For LPG, Consider the case of lethality, Pr=-36.38+2.56 ln tq4/3 Assume t= 82.58 sec. q=10800w/m2 Pr1 = -36.38+2.56 ln 82.58x(10800)4/3 =6.62 From the conversion table Pf1= 0.95 12
VCE of cyclohexane For cyclohexane, Consider the case of 1st degree burning, Pr2=-39.83+3.186ln tq4/3 q=4200 t=9.25 Pr2=-39.83+3.186ln 9.25x(4200)4/3 =2.7 pf2= .01 13
Pool fire model of benzene Pr= a+bln cnt here a=-9.82 b=0.71 n=2 (from World Bank) Assume c=1000ppm t=600 min. Pr3=-9.82+0.71 ln(1000)2 x600 =4.53 pf3=0.32 14
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Individual risk At A IR x,y = f1*pf1+f2*pf2 =8x10-4x0.95+6x10-5x0.01 =7.606x10-4 At B IR x,y = f1*pf1+f2*pf2+f3*pf3 =8x10-6x0.23+6x10-5x.01+2.67x10-4x0.32 =8.46x10-4 16
At C IR x,y = f1*pf1+f3*pf3 =8x10-4x0.95+2.67x10-4x0.32 =8.45x10-4 At D IR x,y = f2*pf2+f3*pf3 =6x10-5x.01+2.67x10-4x0.32 =8.604x10-5 17
Societal risk Assume P a=1000, P b= 2000, Pc=3000, Pd= 4000 N1=P a*pf1+P b*pf1+ Pc*pf1 =1000x0.95+2000x0.95+3000x0.95 =5700 N2=P a*pf2+P b*pf2+Pd*pf2 =1000x0.01+2000x0.01+4000*0.01 =70 N3=P b*pf3+Pc*pf3+Pd*pf3 =2000x0.32+3000x0.32+4000x0.32 =2880 18
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Individual and societal risk

  • 1. PRESENTED BY SRUTHI P M MTECH HSE 1
  • 3. Risk: The likelihood of a specific effect within a specific period. There are two methods of risk determination Qualitative risk determination Quantitative risk determination 3
  • 4. QUANTITATIVE RISK DETERMINATION Risk indices are single numbers or tabulation of numbers which are correlated to the magnitude of risk. Some risk indices are relative values with no specific units, which only have meaning within the context of the risk index calculations. The main two risk sets are Individual risk Societal risk 4
  • 5. Individual risk(IRx,y): Probability of death per year of exposure to an individual at a certain distance from the hazardous source. It is usually expressed in the form of iso-risk contours. IR x,y =裡IR (x,y,i) IR (x,y,i)= 裡fi*pfi Pfi is obtained using probit equation. AlChe/CCPS is used for converting probit equation to probability ie pfi 5
  • 6. Different probit functions used for calculation The probit models are generally expressed as Pr =k1+k2(ln V) Probit equations are available for a variety of exposures, including exposure to toxic materials, heat, pressure and radiation,impact and sound. P=a+bln cnt Esignberg also provides a probit function for fatalities due to direct effect of overpressure as follows. Pr=-77+6.91(ln P0) For first degree burn Pr= -39.83+3.0186ln (q4/3t) For lethality Pr=-36.38+2.56 ln tq4/3 6
  • 7. 7
  • 8. Societal risk: Societal risk is a measure of risk to a group of people. It is most often expressed in terms of the frequency distribution of multiple casualty events. (FN curve). Number of people affected by all incident outcome cases can be estimated using the following equation Ni=裡P (x,y)*pfi 8
  • 9. 9
  • 10. There are three cylinders in a factory. First cylinder is filled with LPG in the horizontal cylinder. Second cylinder is filled with cyclohexane in the vertical cylinder. Third cylinder is filled with Benzene in the vertical cylinder. The wind speed in the region is 4.1 m/s. The ambient temperature is 25C. Determine the individual risk and societal risk. 10
  • 11. Assume the values of frequencies of incident outcome cases as BLEVE of LPG -8x10-4 VCE of cyclohexane -6x10-5 Pool fire of Benzene-2.67x10-4 11
  • 12. BLEVE of LPG For LPG, Consider the case of lethality, Pr=-36.38+2.56 ln tq4/3 Assume t= 82.58 sec. q=10800w/m2 Pr1 = -36.38+2.56 ln 82.58x(10800)4/3 =6.62 From the conversion table Pf1= 0.95 12
  • 13. VCE of cyclohexane For cyclohexane, Consider the case of 1st degree burning, Pr2=-39.83+3.186ln tq4/3 q=4200 t=9.25 Pr2=-39.83+3.186ln 9.25x(4200)4/3 =2.7 pf2= .01 13
  • 14. Pool fire model of benzene Pr= a+bln cnt here a=-9.82 b=0.71 n=2 (from World Bank) Assume c=1000ppm t=600 min. Pr3=-9.82+0.71 ln(1000)2 x600 =4.53 pf3=0.32 14
  • 15. 15
  • 16. Individual risk At A IR x,y = f1*pf1+f2*pf2 =8x10-4x0.95+6x10-5x0.01 =7.606x10-4 At B IR x,y = f1*pf1+f2*pf2+f3*pf3 =8x10-6x0.23+6x10-5x.01+2.67x10-4x0.32 =8.46x10-4 16
  • 17. At C IR x,y = f1*pf1+f3*pf3 =8x10-4x0.95+2.67x10-4x0.32 =8.45x10-4 At D IR x,y = f2*pf2+f3*pf3 =6x10-5x.01+2.67x10-4x0.32 =8.604x10-5 17
  • 18. Societal risk Assume P a=1000, P b= 2000, Pc=3000, Pd= 4000 N1=P a*pf1+P b*pf1+ Pc*pf1 =1000x0.95+2000x0.95+3000x0.95 =5700 N2=P a*pf2+P b*pf2+Pd*pf2 =1000x0.01+2000x0.01+4000*0.01 =70 N3=P b*pf3+Pc*pf3+Pd*pf3 =2000x0.32+3000x0.32+4000x0.32 =2880 18
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